1. Field of the Invention
The invention relates to a secondary-side residual-heat removal system for a pressurized-water reactor, including:
a) a steam generator which is connected into a primary loop of the nuclear reactor by the primary side of its heat-exchanging tubes, PA1 b) a safety condenser to one side of which the secondary side of the steam generator is connected through circuit lines, PA1 c) a water reservoir having a cooling medium which serves for cooling the other side of the safety condenser (tertiary side), wherein the other side of the safety condenser is provided with means for steam removal, and PA1 d) the safety condenser is disposed above the steam generator at such a level that a natural circulation is obtained in residual-heat removal operation through the circuit lines. PA1 a) a steam generator having heat-exchanging tubes with primary and secondary sides, the primary side of the heat-exchanging tubes being connected into the primary loop of the nuclear reactor; PA1 b) a safety condenser having two sides, circuit lines connecting one of the sides of the safety condenser to the secondary side of the steam generator; PA1 c) a water reservoir for receiving a cooling medium for cooling the other of the sides of the safety condenser, the other of the sides of the safety condenser having means for steam removal; PA1 d) the safety condenser being disposed relative to the steam generator at such a level that a natural circulation is obtained during residual-heat removal operation through the circuit lines; PA1 e) a make-up feed device for the secondary side of the steam generator, including a make-up feed tank, in particular for demineralized water, and associated connecting, pressure-relieving and replenishing lines as well as pressure-relieving and shut-off valves.
After shutting down nuclear reactors, so-called residual heat, which is also referred to as decay heat, occurs in all cases of operation and malfunction. In the case of pressurized-water nuclear reactors, the secondary side is used, at least in the initial phase, for the removal of the residual heat, in virtually all cases of operation and malfunction. That takes place by feeding the steam generators with feed water and by discharging energy directly or indirectly into the atmosphere, wherein the energy is transferred in the steam generator from its primary side to the secondary side through its tube bundle.
In order to keep malfunctions under control, a previously known concept for secondary-side residual-heat removal in the installations of pressurized-water nuclear reactors provides an emergency feeding system on the secondary-side feeding side of the steam generators and a steam blow-off device with a blow-control and safety valve on the discharge side. That is disclosed, for example, by German Published, Prosecuted Application DE 24 59 150, corresponding to Published British Application No. 1,525,020 (1); or by Published European Application No. 0 004 167 A3, corresponding to U.S. Pat. No. 4,304,198 (2). In reference (1) it is shown that the respective heat generator is connected by its secondary side not only to its operational feed-water and live-steam lines but also through emergency cooling circuit lines with a condensate recirculation pump to one side of a safety condenser. That safety condenser, which is referred to therein as a residual-heat removal heat exchanger and is equipped with additional condensate cooling means, may be replaced, if appropriate, by a water pool basin. Such a basin is shown in reference (2) and it serves for the blowing off of the secondary-side steam to be cooled, with the water pool being cooled by heat-exchanging tubes which are connected to a cooling circuit. The secondary-side steam is cooled and condensed by blowing off into the water pool. The condensate is recirculated by means of a condensate recirculation pump of the secondary side of the steam generator, i.e. its feed-water space.
Published French Application No. 2 584 228 (3), corresponding to U.S. Pat. No. 4,765,946 (3a), discloses a secondary-side residual-heat removal system for a pressurized-water reactor in which a steam generator, a safety condenser connected to the latter and a water reservoir for the safety condenser are provided. The safety condenser in that case is disposed above the steam generator at such a level that, in residual-heat removal operation, a natural circulation in the circuit lines between the steam generator and the safety condenser is obtained. However, in the case of that known residual-heat removal system, which is referred to as a safety cooling device, the water reservoir is disposed underneath the safety condenser and underneath the steam generator. In order to ensure that the demineralized water can be delivered from the water reservoir into the safety condenser, pressurization and pressure control are used.
As prior art, reference should also be made to Published European Application No. 0 418 701 A1 (4), relating to a system for the removal of decay heat from the core of a pressurized-water reactor. Although in that document a high-level tank is represented in FIGS. 1 and 2, in the case of that known system neither a safety condenser nor a make-up feed device for the secondary circuit is provided.